A differential circuit that processes a differential signal as a countermeasure against common-mode noise is used for communication systems dealing with a high-frequency signal or a high-speed signal. A transmission line having a specific characteristic impedance is used to transmit a high-frequency signal or a high-speed signal. A receiving end of a transmission line is terminated by a resistive element (a termination resistor) having a resistance equal to the characteristic impedance of the transmission line. For example, in an optical-communication system, an integrated circuit includes a differential circuit and a pair of differential input terminals connected to the differential circuit, and a pair of transmission lines is connected to the pair of differential input terminal. Each differential input terminal is terminated to a termination voltage by a termination resistor having a resistance (for example, 50Ω) equal to the characteristic impedance of the transmission line that transmits an input signal to the corresponding differential input terminal Alternatively, the differential input terminals are terminated to a center potential of a differential signal so that a resistance between one terminal and the other terminal of the differential input terminals becomes double of the characteristic impedance (for example, 100Ω). In such an integrated circuit, when the center voltage is generated from a supply voltage by a voltage drop of the resistive element and a resistance of the resistive element is set to be a large value, electrostatic discharge (ESD) resistance of the differential input terminals may relatively decrease.